Fiberboard storage units generally have gained wide acceptance for office use. They are less expensive than units made of wood or metal. They also are relatively light in weight and often are at least partially collapsible, making the units easy to store when not in use or when not yet completely assembled.
Although many fiberboard storage units visually resemble their wood and metal counterparts, their design drastically differs. They usually cannot be assembled with any significant amount of conventional nuts and bolts because the weight of conventional hardware, and the perforations necessary to use such hardware, are detrimental to the strength of these units. Fiberboard units instead are assembled from blanks that are scored and folded, and taped, and the use of screws and bolts is generally avoided. Often panels are folded upon themselves to present an attractive edge and obtain at least a double layer for strength.
Achieving the strength and durability necessary for the end use is a particularly critical problem in the construction of flat files. Their drawers have extreme breadth (the horizontal dimension from side to side) and depth (the horizontal dimension from front to back) and yet the drawers cannot generally be of any great height, it being desirable to store large documents in a plurality of shallow drawers. It is also desirable, however, to form both the drawers and the drawer dividers, or shelves, out of fiberboard. The dimensional requirements of flat files severely tax the natural strength of fiberboard and conventional fiberboard designs.
Adding strength to fiberboard flat files has been a goal long sought after in the field. It has been known in the art to use a reinforcing bar sandwiched between layers of the fiberboard drawer dividers. That this innovation alone was not sufficient is seen by the disclosures of U.S. Pat. No. 3,494,685 that include, in addition to an optional reinforcing bar, an external channelled frame comprising a perimeter frame for the shell, or housing, that engages and supports cross braces for the drawer dividers.
It is desirable, however, to increase the strength of flat files beyond that of these prior art designs without departing significantly from the low cost and convenience of fiberboard construction. It is also desirable to provide both a peripheral frame for the unit's shell and cross frames for the shelves, which frames are not interconnected so that removal of the peripheral frame does not overly diminish the support being given to the shelves that bear the weight of the documents stored in the drawers.